SEATAC, Wash. (AP) — Washington and at least 10 other states, including Iowa, plan to sue the Trump administration over its separation of immigrant families at the U.S.-Mexico border, saying the president's executive order halting the practice is riddled with caveats and fails to reunite parents and children who have already been torn apart.

Washington Gov. Jay Inslee and Attorney General Bob Ferguson made the announcement Thursday outside a federal prison in SeaTac, south of Seattle, where about 200 immigration detainees had been transferred.

At least 10 other states — Iowa, California, Illinois, Massachusetts, Maryland, Minnesota, New Mexico, Oregon and Pennsylvania — planned to join the lawsuit, Ferguson said. New York announced a separate challenge.

In a statement on Twitter, the Iowa attorney general's office said it planned to join the suit, saying the executive order "does nothing to reunify families already torn apart by his administration's policy."

Days before President Donald Trump on Wednesday issued an executive order designed to end the family separation practice, Miller and 20 other attorneys general called on U.S. Attorney General Jeff Sessions and Homeland Security Secretary Kirstjen Nielsen to end "cruel and illegal actions" against children and families seeking asylum.

“Put simply, the deliberate separation of children and their parents who seek lawful asylum in America is wrong,” according to a letter the attorneys general signed. “This practice is contrary to American values and must be stopped.”

Of the detainees in SeaTac, dozens were women separated from their children under the administration's "zero tolerance" policy of prosecuting all migrants caught illegally entering the country.

"This is a rogue, cruel and unconstitutional policy," Washington's attorney general said. "We're going to put a stop to it."

Immigration authorities have separated about 2,300 children from their parents under the policy over the last several weeks, prompting global outrage as images and recordings of weeping children emerged.

Trump signed the order Wednesday after falsely blaming Democrats for the separations and insisting that only Congress could fix the issue.

The order does nothing to reunite those already separated and might require families to remain in custody together longer than allowed under legal precedent, Inslee and Ferguson said. Both Democrats, they accused the administration of denying the parents and children due process; denying the immigrants, many of whom are fleeing gang threats and violence in Central America, their right to seek asylum; and being arbitrary in the application of the policy.

Trump did not directly answer a question to that effect, instead saying: "We have to be very, very strong on the border. If we don't do it, you will be inundated with people and you really won't have a country."

United States Attorney General Jeff Sessions speaking about immigration at Parkview Field in Fort Wayne, Indiana, on June 14, 2018.(Photo: Mike Moore/AP)

The uncertainty is part of the reason legal action remains necessary, Inslee and Ferguson said.

"No one knows what this administration is doing today because they don't know what they're doing today," Inslee said. "These people could not run a two-car funeral."

Ferguson has filed more than two dozen lawsuits against the Trump administration, most notably he successfully sued to block Trump's initial travel ban against several mostly Muslim countries.

He had planned to sue over the family separations in U.S. District Court in Seattle on Thursday, but his office had to rework the complaint after the executive order was issued. It was expected to be filed within a few business days.

All of the states that planned to join in the lawsuit have Democratic attorneys general. Washington, California, Minnesota, Oregon, Pennsylvania and New York have Democratic governors.

"Children belong with their families, not alone and fearful in metal cages," California Attorney General Xavier Becerra said in a written statement. "We are filing this lawsuit because ripping children from their parents is unlawful, wrong and heartless."

A U.S. judge in San Diego is already considering whether to issue a nationwide injunction sought by the American Civil Liberties Union that would order the administration to reunite the separated children with their parents.

Ferguson said his legal team spent much of Wednesday interviewing women who remain in custody after being separated from their children. Some still haven't spoken with their children or don't know where they are.

About 35 of the mothers were transferred this week to the Northwest Detention Center, a privately run immigration jail in Tacoma.

In addition, Ferguson said, his office has so far identified nine children who have been placed in transitional housing in Washington. The state suspects there are more whom officials don't yet know about.